Highly efficient NH3-SCR of NOx over MnFeW/Ti catalyst at low temperature: SO2 tolerance and reaction mechanism

The W modified MnFe/Ti composite oxide catalyst was proposed and tested for low-temperature SCR of NOx by NH3 , which possesses excellent SCR activity, N-2 selectivity and SO2 tolerance compared with MnFe/Ti catalyst. The physicochemical properties of MnFeW/Ti catalyst were comprehensively characterized by N-2 physisorption, XRD, Raman, XPS, NH3-TPD and H-2-TPR. The transport of oxygen and electron became more facile during SCR reaction as a result of the formation of Mn-O-W and Fe-O-W bonds, which was beneficial to maintain the Mn4+ , Fe3+ and chemisorbed oxygen at high relative concentrations and thus accelerated the SCR reaction rate. The appropriate acidity and redox property improved NOx conversion and N-2 selectivity. The in situ DRIFTS results suggested that the surface acidity was tuned via the W doping, leading to that the SCR reaction obeys only Eley-Rideal mechanism. The TG-MS results and DRIFTS spectra revealed that the oxidation of SO2 can be inhibited by restraining the transfer of electrons from SO2 to Mn4+ and Fe3+ , which reduced the formation of metal sul-fates. Therefore, the MnFeW/Ti catalyst exhibits strong SO2 tolerance at low temperature.